One way to duplicate data between a plurality of application systems each made up of a database server and a storage device is to have the DBMSs running on the database servers duplicate the data. A method for duplicating data by use of DBMSs is described in ORACLE9I DATABASE SUMMARY (an Oracle white paper, May 2002). In this technique, the database servers of a plurality of systems are connected to one another, and update information on the DBMS running on one system is transferred to another system to duplicate data.
Another way to duplicate data in a similar system is to use a function to copy data between storage devices. For example, page 5 of a catalog for a Hitachi's integrated storage solution called “Storeplaza” describes the function to copy data between storage devices. Specifically, in this technique, the storage devices of a plurality of systems are connected to one another by way of a fiber channel, and if data on a disk drive of one storage device has been updated, the update is reflected in a disk drive of another storage device.
Implementing a conventional data duplicating method incurs cost higher than that for implementing an ordinary database application.
Furthermore, duplicating data between a plurality of systems in a synchronous manner causes a delay in the application processing.
To duplicate data by use of DBMSs, it is necessary to employ high-performance database servers since the database servers running the DBMSs must take up both the application processing load and the data duplication processing load, resulting in increased cost. Furthermore, to ensure that duplicated data coincides with the original data, synchronous communications must be carried out between the database servers whenever their DBMSs perform update processing. The DBMSs cannot perform subsequent update processing during the synchronous communications, causing a delay in the application processing.
To duplicate data by use of storage devices, on the other hand, it is necessary to connect between the storage devices by way of a broad band line since the entire updated data handled by each DBMS must be duplicated. Use of a broad band line increases the cost. Furthermore, to ensure that duplicated data coincides with the original data, synchronous communications must be carried out between the storage devices whenever data on the disk drives is updated. Subsequent update processing cannot be performed on the disk drives during the synchronous communications, causing a delay in the application processing.
To avoid the delay due to the synchronous communications, there is a method for asynchronously carrying out communications between DBMSs or storage devices. However, when switching to the system on the data duplicating side after a fault or a disaster has occurred (on the data originating side), the data duplicating side must recreate the data that has failed to be transferred, causing a delay in the switching of the systems.